This invention relates to gravity separators, primarily of the kind in which mixed gas, oil and water in a production flow from an oil well are separated by gravity into discrete, vertically spaced, gas, oil and water layers in a separator vessel for subsequent extraction from the vessel by way of a respective gas outlet, oil outlet and water outlet.
It is known to supply the inlet mixture to a gravity separator vessel by way of a gas/liquid cyclone separator which performs a preliminary separation of the inlet mixture into a gas phase and a liquid phase, the liquid phase from the cyclone being discharged into the lower region of the gravity separation vessel, by way of an anti-swirl arrangement.
It is an object of the present invention to improve, in a simple and convenient manner, the separation efficiency of a gravity separator of the kind having a gas/liquid cyclone inlet arrangement.
In accordance with a first aspect of the present invention there is provided a gravity separator comprising a vessel within which a mixture containing oil and water can separate under gravity to form vertically discrete oil and water layers, the vessel having an inlet assembly including a cyclone separator for separating an oil containing inlet flow into gas and liquid phases, said assembly including ducting for receiving the underflow of the cyclone separator and conducting said underflow into that region of the vessel which, in use, is above the water layer.
Preferably the cyclone separator is housed within said vessel and said ducting ensures that the underflow of the cyclone separator is discharged into said region above the water layer even though the underflow outlet of the cyclone separator may be below within the region of the vessel occupied in use by said water layer.
Conveniently the cyclone separator has its overflow outlet within the region of said vessel occupied in use by a gas layer above said oil layer.
Alternatively said cyclone separator is positioned externally of said vessel, said ducting extending through the wall of said vessel to discharge the underflow into said region above the water layer.
In accordance with a second aspect of the present invention there is provided a gravity separator comprising a vessel within which a mixture containing oil and water can separate under gravity to form vertically discrete oil and water layers, the vessel having an inlet assembly including a cyclone separator for separating an oil containing inlet flow into gas and liquid phases, said cyclone separator being positioned inside said vessel with its longitudinal axis inclined out of the vertical by an angle such that It. the underflow outlet of the cyclone separator lies above the region of said vessel occupied by said water layer in use.
Preferably said vessel is intended to accommodate vertically discrete water, oil, and gas layers, and the angle of inclination of the cyclone axis is such, in relation to the length of the cyclone separator, that the overflow outlet of the separator lies in that region of the vessel occupied by the gas layer in use.
Desirably said cyclone separator is arranged with its longitudinal axis in a plane normal to the longitudinal axis of said vessel.
Alternatively said cyclone separator is positioned with its longitudinal axis in a plane containing, or parallel to, the longitudinal axis of said vessel.
In accordance with a third aspect of the present invention there is provided a gravity separator comprising a vessel within which a mixture containing oil and gas can separate under gravity to form vertically discrete oil and gas layers, the vessel having an inlet assembly including a cyclone separator for separating an inlet flow containing oil and gas into gas and liquid phases, and the assembly being arranged to discharge the underflow of the cyclone separator into that region of said vessel which is adjacent the interface of the oil and gas layers in use.
Preferably there is provided ducting for receiving the underflow of the cyclone separator and conducting said underflow into said region of the vessel.
Alternatively said cyclone separator is positioned within said vessel with its longitudinal axis inclined out of the vertical by an angle such that the underflow outlet of the cyclone separator lies in said region of said vessel.
Conveniently the overflow outlet of the cyclone separator discharges externally of the vessel.
Preferably the height within the vessel at which the underflow of the cyclone separator is discharged into the vessel can be adjusted.
Preferably means is provided for dissipating swirl in the underflow prior to its discharge into the vessel.
Conveniently the inlet assembly includes a plurality of cyclone separators.
In accordance with a further aspect of the present invention there is provided a gravity separator comprising a vessel within which a mixture containing oil and water can separate under gravity to form vertically discrete oil and water layers, the vessel having an inlet assembly including a cyclone separator for separating an oil containing inlet flow into gas and liquid phases, the selection of the vessel diameter and the height of the oil/water interface in the vessel, in relation to the positioning and axial length of the cyclone separator, is such that with the cyclone separator positioned generally normal to the plane of the oil/water interface, the underflow outlet of the cyclone separator can discharge directly into that region of the vessel which, in use, is above the water layer in the vessel.
Desirably the discharge of the underflow of the cyclone separator takes place by way of an anti-swirl device.
In accordance with a further aspect of the invention there is provided a inlet assembly for a gravity separator comprising a cyclone separator having a underflow outlet ducting arrangement for discharging the underflow at a region aligned with a position intermediate the axial ends of the cyclone separator.